Parathyroid function in rats treated with growth hormone. A morphometric study.

Male rats weighing 220-250 g were injected i.m. daily with 0.1 mg commercial human growth hormone for 3 days or 12 days. The serum concentration of total calcium phosphorus and alkaline phosphatase were significantly elevated for some days and returned to normal values at the end of the test period. The parathyroid glands, as studied by light and electron microscopical morphometry showed signs of reduced activity at the 4th day and also at the 13th day: a lowered nucleo-cytoplasmic ratio and a decrease of rough endoplasmic reticulum, of Golgi apparatus and of plasmalemmal tortuosity. The findings suggest a hypercalcemic effect of growth hormone involving peripheral organs of calcium metabolism, especially kidney and bone, and a secondary suppression of parathyroid glands by hypercalcemia.20